Frequently Asked Questions (FAQ)¶

EOReader¶

I want to load orthorectified bands, what do I need to do ?¶

EOReader always loads orthorectified bands, you cannot get raw bands !

For Sentinel-3 data, EOReader uses SNAP to geocode the wanted images.
For SAR images, EOReader uses SNAP to orthorectify the wanted images.
For DIMAP data, if not already orthorectified, EOReader will use gdalwarp through rasterio (with RPC_DEM keyword) to orthorectify the DIMAP stack.
However, this comes with several limitations:
- Pay attention to give a sufficiently resolute DEM (does orthorectifying Pleiades data with a 30m SRTM DEM make sense ?)
- gdalwarp cannot access DEM through S3-compatible storage or https links. Be sure to link a DEM stored on disk.
For other sensors, non-orthorectified bands are not supported yet.

I want to load projected bands, what do I need to do ?¶

EOReader always loads projected bands (in UTM). This may be an issue for:

Sentinel-3 data that are very wide and may have inaccurate georeferencing.
DIMAP data provided in WGS84 that need reprojection (and therefore time-consuming processes)

If needed, we could change this to allow WGS84 representation. If so, do not hesitate to open an issue on GitHub !

SNAP¶

SNAP DEM vs other DEM¶

SNAP has a capability to use its own DEMs. This does not interfere with the DEM provided to load a DEM band for example.

However, you can force SNAP to use your own DEM (stored in EOREADER_DEM_PATH, providing your DEM is compatible) by setting the environment variable EOREADER_SNAP_DEM_NAME to External DEM.

What SNAP’s GPT optimizations are you using ?¶

We are using some optimizations in order to optimize SNAP’s GPT speed, as specified here

Memory: We are allowing GPT to use 95% of your max virtual memory
CPU: We are allowing GPT to use max_core - 2 cores of your computer (i.e. 14 cores out of 16)
Tiles: Width and height are set to 2048 pixels (instead of 512x512) and cache to 50% of your max memory (instead of 1024Mo)

Known SNAP bugs¶

Sometimes SNAP process returns Feature 'http://javax.xml.XMLConstants/feature/secure-processing' is not recognized. This is a known SNAP bug. Just add the line -Djavax.xml.parsers.SAXParserFactory=com.sun.org.apache.xerces.internal.jaxp.SAXParserFactoryImpl to your gpt.vmoptions file. Please look at this issue for more information.